Micromechanical yaw rate sensors are used in the automotive field, for example, in electronic stability program (ESP) systems, for rollover sensing, or for navigational purposes. The function of the yaw rate sensor is the correct measurement of the automobile movement around a rotational axis.
A typical micromechanical yaw rate sensor normally includes an oscillating body, which is situated so it is movable on a substrate, and may be set into an oscillating movement in relation to the substrate at a drive frequency fx. A rotary motion of a rotatable body, on which the yaw rate sensor is fastened, which is nonparallel to the oscillating movement induces a Coriolis force on the oscillating body, by which the oscillating body is additionally deflected. With the aid of measuring electrodes, this additional deflection may be detected capacitively and evaluated with respect to a variable describing the rotary motion of the rotatable body. Such a variable is a yaw rate of the rotary motion of the rotatable body, for example.
In the above-described measurement principle, linear (i.e., non-rotational) accelerations or vibrations on the rotatable body also cause a deflection of the measuring electrodes using a force which acts parallel to the Coriolis force. Various methods are known for differentiating rotary motions from such a linear acceleration.
Firstly, coupling two yaw rate sensor elements designed as linear oscillators in such a way that their oscillating bodies oscillate antiparallel to one another is known. In such a system, a linear acceleration or vibration (without a rotational component) results in forces having identical force vectors acting on the measuring electrodes, while, in contrast, in the case of a rotary motion, the force vectors of the Coriolis forces acting on the measuring electrodes are opposite to one another. If the output signals of the two sensor elements are subtracted from one another, the (in-phase) signal components of the two sensor elements, which are caused by linear acceleration or vibration, cancel one another out, while, in contrast, the (counter-phase) signal components, which are caused in the case of a rotary motion by Coriolis forces, do not cancel one another out through the subtraction. The influence of linear accelerations or vibrations on the sensor may thus be compensated for.
However, complete compensation occurs in such a system only if the two sensor elements are laid out perfectly symmetrically to one another. Because of manufacturing tolerances, and the like, however, certain asymmetries are unavoidable, so that a differential signal arises in the case of a linear interference, which is typically not differentiable from yaw rate signals.
A low-pass filter provided on the output side may be used for the purpose of filtering out such signal components caused by linear interference. However, the problem exists that in the event of vibrations having a frequency which is approximately equal to drive frequency fx of the sensor, a sideband arises, which may pass through the low-pass filter and may therefore be incorrectly interpreted as a rotational component. In other words, a possibility of interference exists in the event of vibrations in a frequency range of drive frequency fx plus/minus the cutoff frequency of the output-side low-pass filter.
In order to counteract the possibility of interference in this frequency range, damping of the external vibrations may be provided in this frequency range, e.g., by a suspension having suitable spring elements. However, such measures are complex and also cannot achieve complete compensation of the vibrations.